Question

The magnetic field at a distance \( r \) from a long wire carrying current is 0.4 tesla. The magnetic field at a distance \( 2r \) is:

• A. 0.2 tesla
• B. 0.8 tesla
• C. 0.1 tesla
• D. 1.6 tesla

Hint:

The magnetic field due to a long wire carrying current is inversely proportional to the distance from the wire.

Answer 1

The Correct Option is A

Step 1: Magnetic field due to current.
The magnetic field \( B \) due to a long straight wire is inversely proportional to the distance \( r \): \[ B \propto \frac{1}{r} \] Step 2: Calculation at \( 2r \).
If the magnetic field at \( r \) is 0.4 tesla, at \( 2r \), the magnetic field will be: \[ B_{\text{new}} = \frac{0.4}{2} = 0.2 \, \text{tesla} \]
Final Answer: \[ \boxed{0.2 \, \text{tesla}} \]